Integrated Sensing for IPMC Actuators Using Strain Gages for Underwater Applications

Ionic polymer-metal composite (IPMC) actuators have many advantages, for instance, they: 1) can be driven with low voltages (<;5 V); 2) are soft, flexible, and easily shaped; and 3) can operate in an aqueous environment (such as water). Important applications for IPMCs include active catheter devices for minimally invasive surgery, artificial muscles, and sensors and actuators for biorobotics. Due to inherent nonlinear behavior, dynamic effects, and external disturbances, sensing and feedback control are required for precision operation. A new method to sense the displacement of an IPMC actuator using resistive strain gages is proposed. The sensing scheme is low cost, practical, effective, and importantly, compact compared to existing methods such as lasers and charge-coupled device (CCD) cameras. The strain-to-displacement relationship is developed and experimental results are presented to demonstrate the effectiveness of the sensing scheme. Furthermore, the sensor signal is used as feedback information in a repetitive controller to improve the tracking of periodic motion. The stability condition for the controller is presented, and the sensing scheme and feedback control approach are applied to a fabricated perfluorinated ion-exchange-membrane-based IPMC actuator with lithium as its counterion. Experimental results show that the tracking error can be reduced by approximately 50% compared to PID control for tracking of periodic signals, including sinusoidal and triangular wave forms.